Inorganic-organic resins based on polyisocyanates and aqueous alkali metal silicate solutions are already known and have been described, for example, in German Offenlegungsschriften Nos. 1,770,384; 2,227,147; 2,359,606; 2,359,607; 2,359,608; 2,359,609; 2,359,610; 2,359,611 and 2,359,612; and, German Auslegeschrift No. 2,310,559.
One of the main advantages which these materials have over purely organic materials is their improved fire resistance due to their inorganic constituents. Depending on their composition and the reaction conditions employed, they may be foamed or noncellular products, hard or soft, brittle or flexible. Due to the wide range of variation of the properties of these inorganic-organic materials, they have a wide range of possible applications.
Although the reaction speed obtained when mixing polyisocyanates and alkali metal silicates can be directly influenced by the alkalinity of the aqueous/alkali metal silicate solution, the nature of the selected polyisocyanate, the temperature, the intensity and duration of the mixing process, and the like, it is often desirable to use catalysts as well, particularly for producing inorganic-organic foams.
It has previously been known for this purpose to use catalysts such as tertiary amines; silaamines; tetraalkyl ammonium hydroxide, alkali metal hydroxides; alkali metal phenolates; alkali metal alcoholates; hexahydrotriazines and organic metal compounds, particularly organic tin compounds, which are normally used for the production of polyurethane foams. Tertiary amines were preferably used, and these could in addition contain hydrogen atoms which were reactive with isocyanate groups. In the examples given in German Offenlegungsschrift No. 1,770,384, for example, one of the catalysts used was an amine catalyst (mixture of 3 parts of N-.beta.-hydroxyethyldimethylamine and 1 part of triethylene diamine)
One disadvantage of such catalysts, however, is that when mixed with isocyanates they are not stable in storage because they frequently promote the reaction of isocyanate groups with each other even at room temperature, thus giving rise to an undesirable increase in the viscosity of the mixture during storage. Moreover, the amines used are generally insoluble in concentrated aqueous alkali metal silicate solutions because of the basic nature of aqueous alkali metal silicates. The amines either separate when left to stand for a short time or may even decompose.
These difficulties in the production of inorganic-organic plastics has been generally overcome by emulsifying the catalysts in the aqueous alkali metal silicate component, by dissolving them in the polyisocyanate shortly before the alkali metal silicate component is mixed with the polyisocyanate, or by adding the catalysts through a separate feed device.
All these methods, however, are unsatisfactory from a commercial and economical point of view. The separate addition of catalyst is often quantitatively inaccurate due to the very small proportion of catalyst used relative to the other reactant. Moreover, the catalyst must in some cases be used as a third component so that commercial two-component feeding devices cannot be used. If the catalysts, on the other hand, are first mixed with the aqueous alkali metal silicate solutions, the time taken for mixing must not be more than a few minutes because otherwise phase separation may take place, for example between the organic amine and the aqueous basic phase. Even the use of hydrophilic amines such as triethanolamine does not obviate this difficulty.
Another disadvantage of using tertiary amines is that most of them have an unpleasant smell. The organo-metallic catalysts frequently used in polyurethane chemistry, such as tin(II) octoate or dibutyl tin dilaurate, are also hardly suitable for the commercial production of inorganic-organic resins because they are either insoluble in the aqueous alkali metal silicate solutions or decomposed by them. Hexahydrotriazines, tetraalkylammonium hydroxide and silaamines also show signs of incompatibility, i.e., insolubility or decomposition in concentrated alkaline aqueous silicate solutions.
When alkali metal hydroxides, alkali metal phenolates and alkali metal alcoholates are used as catalysts, the inorganic-organic products obtained are frequently unsatisfactory in their use properties, and, in particular, are often sandy or brittle with little mechanical strength.
It is, therefore, an object of the present invention to substantially overcome the disadvantages attending the use of the known catalysts and to discover catalysts which have the advantage of being soluble and stable in storage in the polyisocyanate and which give rise to high quality inorganic-organic resins, and, particularly foams, when mixed with aqueous basic solutions.